1. Field of the Invention
The present invention relates to a crystal oscillator having a function of outputting a stable oscillating waveform for various specifications.
2. Description of the Related Art
There are communication methods for cellular phones including PDC (Personal Digital Cellular) which is used in Japan, GSM (Global System for Mobile Communication), and CDMA (Code Division Multiple Access), and there are various specifications for types of cellular phones using the same communication method. For crystal oscillators for temperature control which are mainly used for cellular phones, oscillation output characteristics capable of responding to specifications of all the sets are required.
Hereinafter, a general crystal oscillator TCXO for temperature control will be described. FIGS. 6 and 7 are circuit diagrams showing configurations of the general crystal oscillator TCXO.
Referring to FIG. 6, an output terminal of an oscillator 1 having a quartz vibrator is connected to an input terminal of an inverter 2, an output terminal of which is connected to an input terminal of a first transistor 3 and an input terminal of a second transistor 4. In addition, an output terminal of the first transistor 3 and an output terminal of the second transistor 4 are connected to an oscillation output terminal 5, and an external load element 6 is connected to the oscillation output terminal 5.
Referring to FIG. 7, an output terminal of an oscillator 1 having a quartz vibrator is connected to an input terminal of an inverter 2, an output terminal of which is connected to one terminal of a first resistor 7 and one terminal of a second resistor 8. In addition, the other terminal of the first resistor 7 is connected to one terminal of a first capacitor 9 and the input terminal of the first transistor 3, and the other terminal of the first capacitor 9 is grounded. In addition, the other terminal of the second resistor 8 is connected to one terminal of a second capacitor 10 and the input terminal of the second transistor 4, and the other terminal of the second capacitor 10 is grounded.
In addition, the output terminal of the first transistor 3 and the output terminal of the second transistor 4 are connected to an oscillation output terminal 5, and an external load element 6 is connected to the oscillation output terminal 5.
Hereinafter, the operation of the crystal oscillator TCXO configured as described above will be described.
In the crystal oscillator TCXO shown in FIG. 6, a stable oscillation frequency is generated from the oscillator 1 having the quartz vibrator, and frequency signals at a part A2 of the input terminal of the second transistor 4 and a part A1, in which a signal is phase-inverted by the inverter 2, are phase-inverted from each other. By alternatingly operating the first transistor 3 and the second transistor 4, a stable oscillation signal having a constant amplitude is output to the oscillation output terminal (A3) 5.
Since specifications including a load of an output part and harmonic characteristics are different depending on a set such as a cellular phone to which a crystal oscillator is installed, the optimization of an output waveform is acquired in the crystal oscillator TCXO shown in FIG. 7 by inserting passive elements such as the resistors 7 and 8 or the capacitors 9 and 10 to the part A1, in which a signal is phase-inverted by the inverter 2, the part A2 of the input terminal of the second transistor 4, and the like to delay the rise or fall of the output signal.
As the external load element 6 which is connected to an external circuit, a circuit represented by a bypass condenser Cp, a load capacitor CL, a load resistor RL, and the like which are shown in FIG. 8 as an equivalent circuit is used.
Patent Document 1: JP11-17452
Patent Document 2: JP9-294066
In a general configuration, it is possible to optimize an output waveform by arranging passive elements such as resistors 7 and 8 or capacitors 9 and 10 to the part A1, the part A2, and other parts as described above or the like according to the specifications of a set to which the crystal oscillator is installed, but the characteristics become far off the optimized characteristics for a set having different specifications.
However, to develop one IC (Integrated Circuit) for each of the specifications is inefficient and causes the managing operation complicated, and in a case where one IC is designed to satisfy a plurality of different specifications, the IC cannot show proper characteristics due to its in-between characteristics.